Earth Hour, a global environmental initiative to get people thinking about climate change, saw people turning off the lights all over the world for an hour on Saturday evening.
It took place from 8:30 p.m. to 9:30 p.m. local time all over the world.
The World Wildlife Fund said more than a billion people in 100 countries are expected to participate.
The WWF blog reported that Russian cyclists went for a ride with head lamps. "These cyclists are heroes," the group's Russia office said. "In Moscow, it is – 8 [C] degrees."
In Egypt, the Earth Hour word was spread by social media.
Greece and China turned off the lights on famous monuments, including the Great Wall of China, which seemed to make the massive structure disappear. European cities went dark as citizens turned off house lights.
In Canada, Jennifer Anne Temple posted on the WWF blog that she and her husband will use a "crank up" table lamp, a "crank up" radio, and use head lamps when moving around the house.
"We just pour a couple of glasses while listening to jazz radio. It may be the best quality time hubby and I share all year, just chatting and music," she wrote.
Nova Scotia Power said its officials saw an 18-megawatt reduction in power consumption in the hour after 8:30 p.m. "representing the equivalent of turning off approximately 1.4 million 13-watt compact fluorescent light bulbs."
A crowd in Toronto watched as billboards in the city's downtown Dundas Square went dark. But some said they were disappointed that some stores remained brightly lit.
Earth Hour began in 2007 in Sydney, Australia.